Apparatus for determining the hot tearing susceptibility of metallic melts

ABSTRACT

The present invention relates to an apparatus for determining the hot tearing susceptibility of metallic melts, comprising a casting mould, which has a first subvolume and a second subvolume, the second subvolume being formed as a tubular portion with a first end and a second end, the first end being connected to the first subvolume, comprising a measuring element, which extends into the second end of the tubular portion, and comprising a measuring device for recording a force on the measuring element and/or a change in position of the measuring element in the direction of extent of the tubular portion, the measuring device being coupled with the measuring element. The object of allowing an improved quantitative and qualitative determination of hot tearing susceptibility is achieved by the cross-sectional area of the tubular portion being reduced in the direction of the second end in each and every subportion of the tubular portion that may be selected substantially over the entire length.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority from GermanPatent Application Serial No. DE 10 2008 031 777.2, filed Jul. 4, 2008,the entire disclosure of which is hereby incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for determining the hottearing susceptibility of metallic melts, comprising a casting mould,which has a first subvolume and a second subvolume, the second subvolumebeing formed as a tubular portion with a first end and a second end, thefirst end being connected to the first subvolume, comprising a measuringelement, which extends into the second end of the tubular portion, andcomprising a measuring device for recording a force on the measuringelement and/or a change in position of the measuring element in thedirection of extent of the tubular portion, the measuring device beingcoupled with the measuring element.

2. Discussion of the Prior Art

Hot tearing is a significant problem in the solidification of metallicmelts. Hot tearing is the term used for intercrystalline orinterdentritic discontinuities which occur during the solidifying ormelting in a temperature range between solidus temperature and liquidustemperature. Hot cracks may be microscopically small or extend overseveral millimetres or even centimetres. In any event, they represent adefect for a workpiece that is intended to be created at least partiallyfrom a solidified metallic melt.

In particular with regard to strip casting or comparable continuouscasting processes, knowledge of the hot tearing susceptibility of a meltis of great significance, since this has a direct influence on thestrength of the cast product. This knowledge is also of significance forwelds or the use of certain welding methods, since it has a directinfluence on the durability of the weld.

In the past, there has been considerable activity in determining the hottearing susceptibility of steels and aluminium alloys in particular.However, there has not so far been any success in sufficientlyunderstanding or even simulating the phenomenon of hot tearingsusceptibility. There is also no apparatus with which hot tearingsusceptibility can be reliably determined.

When dealing with a solidification process of a metal melt in a castingmould, the typical approach so far has been to measure, and consider inthe evaluation, not only the chemical composition but also meltingparameters such as the melting bath temperature, the casting mouldtemperature, the variation in the temperature during the solidificationand the forces occurring during the solidification in the casting mouldas a result of shrinkage. A purely qualitative assessment may also bemade by visual observation of the material in the region of theoccurrence of a crack, its size and morphology.

A hot crack is qualitatively characterized with respect to its size. Adistinction is generally drawn between cracks that can be seen with thenaked eye, cracks that can be made visible with the aid of some meanssuch as a magnifying glass and cracks that can only be seen under amicroscope. The length of the crack is also often used as a criterionfor hot tearing susceptibility. The known test methods have in commonthat, although they can assess the occurrence of cracks and their size,they do not allow conclusions to be drawn with respect to strains, andconsequently with respect to resultant stresses. However, the knowledgeof strains and stresses allows the susceptibility to cracks occurring inthe future to be qualitatively determined or their further behaviour tobe predicted.

Hot tearing susceptibility has so far been qualitatively determined bymeans of casting moulds in which, for example, a flow length ismeasured. The length of the solidified material up to which no crackoccurs serves here as a characteristic number. This numerical value isspecific to the geometry of the casting mould, i.e. the cross section ofthe casting channel and the chosen sprue system. Also specific to therespective test setup is the material from which the casting mould isproduced. This may be, for example, either steel, if for example thecasting mould is designed as a permanent mould, or sand. In the lattercase, the grain size of the sand, the grain size distribution, themoisture content, the binder and the compaction and composition of thesand are also to be taken into consideration as further parameters. Themelting bath temperature and the casting mould temperature are alsodetermined as additional characteristic values.

A known casting mould for determining hot tearing susceptibility isbased on annular geometries, in which the outside diameter is keptconstant while the inside diameter can be varied. During thesolidification, the material shrinks onto the core and, depending on thewall thickness, melting bath temperature, casting mould temperature andchemical composition, cracks can form. Problems with this type ofcasting mould occur in particular in the region of the sprue, since theconditions are often not reproducible there.

In S. Instone et al., “New apparatus for characterizing tensile strengthdevelopment and hot cracking in the mushy zone”, International Journalof Cast Metals Research 12 (2000) 441-456, there is a description of anH-shaped casting mould with the sprue in the centre, in the case ofwhich a tensile testing machine is also incorporated in the system. Thisis used to incorporate a force and attempt to draw conclusions withrespect to the hot tearing susceptibility, while taking intoconsideration the crack occurring under a certain force and knowntemperature profiles.

Apart from that, casting moulds with a first receiving volume and atubular measuring volume are also in use. In the case of these moulds,hotspots usually occur in the connecting region between the firstreceiving volume and the tubular measuring volume. A hotspot is anaccumulation of melt during the solidification process that usuallyoccurs in the central region of the volume of the casting mould that isfurthest away from the cold wall of the casting mould. In the case ofthese casting moulds, the shrinkage behaviour of the melt duringsolidifying is measured over the length of the bar. Here too, parametersare the melting bath and casting mould temperature and the chemicalcomposition of the melt. The hot tearing susceptibility is additionallyinfluenced by the thermal content of hotspots.

An apparatus according to the precharacterizing clause of the claim isdescribed in G. Cao, S. Kou, “Hot tearing of ternary Mg—Al—Ca alloycastings”, Metallurgical and Materials Transactions 37A (2006)3647-3663. In it, Cao and Kou describe a direct measurement of thestrains occurring during the solidification and the resultant forceswith a bar-shaped subvolume of a casting mould. Y. Wang et al., “Anunderstanding of the hot tearing mechanism in AZ91 magnesium alloy”,Materials Letters 53 (2002) 35-39, also describe a test setup with abar-shaped casting mould geometry for determining hot tearingsusceptibility.

However, with the apparatuses used, considerable frictional forces occurbetween the solidifying material and the inner wall of the castingmould, dependent on the temperatures of the solidifying material and ofthe casting mould, and ultimately on the shrinkage behaviour of both.Lubricants that are used under some circumstances bring with themfurther difficulties in the interpretation of the measured values. Ameaningful interpretation is scarcely possible with frictional forcesoccurring in this way.

All the apparatuses known so far do allow a certain assessment of hottearing susceptibility. However, because of the frictional forcesoccurring, none is suitable for the precise quantitative and qualitativedetermination of hot tearing susceptibility.

SUMMARY

It is therefore the object of the present invention to provide anapparatus for determining the hot tearing susceptibility of metallicmelts that allows an improved quantitative and qualitative determinationof the hot tearing susceptibility of various metallic melts.

The present invention provides an apparatus for determining the hottearing susceptibility of metallic melts, comprising a casting mould,which has a first subvolume and a second subvolume, the second subvolumebeing formed as a tubular portion with a first end and a second end, thefirst end being connected to the first subvolume, comprising a measuringelement, which extends into the second end of the tubular portion, andcomprising a measuring device for recording a force on the measuringelement and/or a change in position of the measuring element in thedirection of extent of the tubular portion, the measuring device beingcoupled with the measuring element, characterized in that thecross-sectional area of the tubular portion is reduced in the directionof the second end in each and every subportion of the tubular portionthat may be selected substantially over the entire length.

Here, the term “casting mould” covers all receptacles that are suitablefor a metallic melt to be contained or received in an inner volume orcreated therein.

Here, the term “volume” essentially means the inner volume that isavailable for receiving melts. The inner volume of the casting mould ismade up here of at least two subvolumes.

The characterizing feature that the cross-sectional area of the tubularportion is reduced in the direction of the second end in each and everysubportion of the tubular portion that may be selected substantiallyover the entire length is to be interpreted essentially as meaning thatthere is substantially no subportion over the entire length of thetubular portion in which the cross-sectional area is constant in thedirection of extent of the tubular portion. This avoids falsification ofthe measurement by frictional forces between the solidifying materialand the wall of the casting mould. For example, the tubular portion mayhave a circular cross section, with the diameter being reduced in everysubportion towards the second end, and so the portion is frustoconical.

As compared with known measuring apparatuses, the apparatus according tothe invention has the advantage in particular that the shrinking of thesolidifying material in relation to the casting mould, which has aneffect primarily in the direction of extent of the tubular portion,leads to the solidifying material immediately becoming detached from thewall of the casting mould, and consequently no frictional effectsbetween the solidifying melt and the wall of the casting mould beingmeasured.

Furthermore, the measurement is independent of the shrinkage behaviourof the casting mould itself, since the melt in the casting mouldsgenerally shrinks more than the material of the casting mould itself.

The apparatus according to the invention has been developed primarilyfor determining the hot tearing susceptibility of magnesium melts.However, as a result of the test setup and the characteristic valuesdetermined, the apparatus can be used not only for magnesium alloys butalso for aluminium, zinc and non-ferrous metals and for steels and othermetallic melts.

The geometry according to the invention and the possibility of using awide variety of casting mould materials mean that the apparatusessentially allows measurements on all materials during solidification.Consequently, a standardizable measuring cell for determining hottearing susceptibility is available for the first time. Not only aqualitative assessment but at the same time also a quantitativeassessment is therefore possible. This also allows for the first timethe direct comparison of the hot tearing susceptibility of a widevariety of materials.

A great advantage of the invention is the simultaneous detection ofcracks and the resultant changes in strain or stress in a test sample.Both quantitative and qualitative findings can be reached with respectto hot tearing susceptibility.

Apart from the chemical composition, melting parameters such as meltingbath temperature, casting mould temperature, variation of thetemperature during the solidification and the forces occurring duringthe solidification in the casting mould due to shrinkage are alsomeasured with the apparatus and taken into consideration in theevaluation. In addition, a purely qualitative assessment of the materialcan be made at the same time with respect to the occurrence of a crack,its size, morphology and behaviour over time.

In order to minimize hydrostatic pressure influences or other influenceson the measurement caused by gravitational force, it is advantageous ifthe tubular portion extends substantially in a horizontal direction.

Temperature measuring elements are preferably arranged along thedirection of extent of the tubular portion. These may on the one handserve for recording the temperatures for evaluation purposes. On theother hand, they may be used for regulating the temperature of the wallof the casting mould, and correspondingly the temperature of thesolidifying melt. For this purpose, it is of advantage if at least onetemperature measuring element is arranged in the first subvolume. Thismay, for example, be telescopically insertable into the inner volume ofthe casting mould, in order that the temperature at the hotspot in theconnecting region between the first and second subvolumes can bemeasured.

It is advantageous for the temperature regulation and control if thefirst subvolume and/or the tubular portion is provided with a heatingdevice and/or a cooling device. This allows the solidification processof the melt to be controlled in a specific manner. It is particularlyadvantageous in this respect if the temperature of the tubular portioncan be controlled in such a way that the second end is colder than thefirst end, and consequently the melt solidifies first at the second endand thereby becomes connected to the measuring element in atension-resistant manner. This allows the measurement of the tensileforce that is caused by the shrinkage behaviour of the melt to becarried out accurately from the earliest possible stage of thesolidification process.

A venting opening is preferably provided at the second end of thetubular portion, in order that the air in the tubular portion, whichpreferably extends substantially in a horizontal direction, can escapewhen the melt enters the portion. This venting opening may be, forexample, a notch in the measuring element that extends on the upper sidein the direction of extent of the measuring element.

The apparatus preferably has a sprue system located at least partiallyabove the casting mould, the first subvolume of the casting mould beingdesigned for receiving a metallic melt from the sprue system. In thiscase, the melt is created in the sprue system and, when the melt and thecasting mould are at a suitable temperature, the melt is let out througha lower outlet into the first subvolume of the casting mould. Therefore,the first subvolume advantageously has an upper opening for receivingthe melt from the sprue system located above it. As soon as the level ofthe melt has reached the connecting region between the first subvolumeand the second subvolume of the casting mould, the melt is alsodistributed into the second subvolume.

In order that the measuring element can move in the axial directionwithout friction as far as possible, it is guided in relation to thecasting mould, preferably in a sleeve, for example made of graphite orceramic, with little frictional contact.

For the reading out and evaluation of the measurement results, themeasuring device and any temperature measuring elements are preferablyconnected to a computer-controlled readout system and can be read outwith this system.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription of the preferred embodiments. This summary is not intendedto identify key features or essential features of the claimed subjectmatter, nor is it intended to be used to limit the scope of the claimedsubject matter.

Various other aspects and advantages of the present invention will beapparent from the following detailed description of the preferredembodiments and the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Advantageous embodiments of the invention are explained in detail belowon the basis of FIGS. 1 to 4.

FIG. 1 schematically shows the setup of an advantageous embodiment ofthe apparatus according to the invention.

FIG. 2 shows a vertical longitudinal section through a casting mould ofan advantageous embodiment of the apparatus according to the invention.

FIG. 3 shows a horizontal longitudinal section through a casting mouldof an advantageous embodiment of the apparatus according to theinvention.

FIG. 4 shows a measurement result in the form of a graph, in which themeasured tensile force and the temperature over time for two differenttests are plotted.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is susceptible of embodiment in many differentforms. While the drawings illustrate, and the specification describes,certain preferred embodiments of the invention, it is to be understoodthat such disclosure is by way of example only. There is no intent tolimit the principles of the present invention to the particulardisclosed embodiments.

FIG. 1 schematically shows the overall setup of an apparatus fordetermining the hot tearing susceptibility of metallic melts. The maincomponents of the apparatus are arranged on a stable horizontal platform1. Extending vertically from the horizontal platform 1 to the side is aholding device 3, which serves for fastening a sprue system 5 above acasting mould 7. The sprue system 5 substantially comprises acylindrical receptacle, which is designed as a melting furnace 9 with aheatable wall. The melting furnace 9 has an upper opening, which can beused for filling with the metallic material 10, which can be meltedinside the melting furnace. After filling, the upper inlet opening canbe closed with a cover 11. On the underside, the melting furnace 9 hasan outlet opening 13, which can be opened and closed with a closuresystem 15. In this embodiment, the closure system 15 is a plug 17, whichcan be raised and lowered by means of a vertically extending rod 19,which on the upper side is led out from the melting furnace 9 to theoutside through a central bushing in the cover 11. In the loweredposition of the plug 17 that is shown in FIG. 1, the outlet opening 13on the underside is closed, and no metallic melt 10 can leave. Forregulating the heating temperature and/or for determining when themetallic melt 10 has reached the suitable temperature, a temperaturemeasuring element 21 is endoscopically or telescopically immersed in themetal melt 10 through the cover 11. For this purpose, the temperaturemeasuring element 21 is connected via a communication link to a readoutsystem 25 controlled by a computer 23.

Arranged underneath the outlet opening 13 of the melting furnace 9 isthe casting mould 7, so that, when the plug 17 is raised, the melt 10can flow through the outlet opening 13 into the casting mould 7. Thecasting mould 7 has two subvolumes, the first subvolume 27 beingsubstantially a cylindrical receptacle with an opening on the upper sidefor receiving the melt 10 from the melting furnace 9. A second subvolume27 extends in the form of a tubular portion 29 substantiallyhorizontally away from the first subvolume 27. The tubular portion 29has a first end 31, which is connected to a lower region of the firstsubvolume 27, and a second end 33, into which a measuring element 35extends. When the casting mould 7 is filled from the melting furnace 9on the upper side, the first subvolume 27 fills first, until a fillinglevel at which the melt 10 flows into the tubular portion 29 is reached.For a measurement, the tubular portion 29 must be completely filled.

It can be seen still more clearly in FIGS. 2 and 3 that thecross-sectional area of the tubular portion 29 is reduced in thedirection of the second end 33 in each and every subportion of thetubular portion 29 that may be selected substantially over the entirelength. In this embodiment, the diameter of the circular cross-sectionalarea is reduced over the entire length of the tubular portion 29 with ataper angle from the first end 31 towards the second end 33 ofapproximately 3°.

A large part of the outer surface area of the casting mould 7 isequipped with a heating or cooling system 37, so that the temperature ofthe casting mould 7 can be suitably controlled both in the firstsubvolume 27 and in the tubular portion 29. This allows thesolidification behaviour of the melt 10 in the casting mould 7 to becontrolled in a specific manner. For regulating the heating or coolingsystem 37 and for evaluation purposes, the casting mould 7 is alsoequipped with temperature measuring elements 39, 41, 43, 45, 47, whichare respectively connected via a communication link to thecomputer-controlled readout system 25. A temperature measuring element39 measures the temperature of the first subvolume 27 of the castingmould 7. Three temperature measuring elements 43, 45, 47 measure thetemperature of the tubular portion 29 in various regions along thedirection of extent of the tubular portion 29. A temperature measuringelement 47 is in this case arranged at the second end 33 of the tubularportion 29. A temperature measuring element 41 is telescopically orendoscopically led through the first subvolume 27 into the connectingregion between the first subvolume 27 and the tubular portion 29. Thisallows the temperature measuring element 41 to be used for measuring thetemperature of the melt 10 at the hotspot.

At the second end 33 of the tubular portion 29 is the measuring element35, which extends substantially in the form of a piston coaxially in thedirection of extent of the tubular portion 29 and is guided in relationto the casting mould 7 in a sleeve 49 with little frictional contact,for example made of graphite or ceramic. The measuring element 35 istherefore mounted movably in the axial direction. For reading out theforce and/or the position in the direction of extent of the tubularportion 29, the measuring element 35 is coupled with a measuring device51. The measuring device 51 has in this case a universal joint 53 and arod-shaped transmission element 55, the universal joint 53 connectingthe measuring element 35 to the transmission element 55. Thetransmission element 55 transmits the force and/or the change inposition in the axial direction to a force or position measuringinstrument 57. The force or position measuring instrument 57 is likewiseconnected via a communication link to the computer-controlled readoutsystem 25 for the reading out and evaluation of the measurement data.

The casting mould 7 and the force or position measuring instrument 57have defined positions with respect to the platform 1, to which they arepreferably fixedly connected. The casting mould 7 and/or the force orposition measuring instrument 57 may also be connected to the platform 1movably in the direction of extent of the tubular portion 29. Thisadmittedly then necessitates a precise calibration of the axialpositions. However, an additional tearing force can then be exerted onthe melt 19, for example by means of a controlled stepping motor, inorder to provoke a crack and/or to measure the load-bearing capacity ofthe material under certain stresses. Similarly, the sprue system 5 maybe connected to the holding device 3 in a vertically adjustable manner,in order that during the initial casting the drop height of the melt 10can be set and can be adapted appropriately to the material used. Theoverall apparatus may be designed, for example, as a benchtop experimentwith a lateral extent of less than 1 metre. The tubular portion 29,tapering towards the second end 33, may have, for example, a length ofapproximately 20 cm and a diameter of between 12 and 8 mm.

FIGS. 2 and 3 respectively show a vertical and a horizontal longitudinalsection through the casting mould 7. The taper angle θ of the tubularportion 29 from the first end 31 towards the second end 33 is shown forclarification. The second end 33 of the substantially horizontallyextending tubular portion 29 is supported from below by a support 59,which is connected to the platform 1, to which the first subvolume 27 ofthe casting mould 7 is also connected. The measuring element 35 has onthe upper side a venting opening 61, in the form of a notch, extendingin the direction of extent of the measuring element 35. The ventingopening 61 allows the venting of the substantially horizontallyextending tubular portion 29 during the filling with the melt 10.

With the apparatus shown, the method described below for determining thehot tearing susceptibility of a metallic melt is performed. First, ametallic material 10 of a known chemical composition that is to betested, for example magnesium with an aluminium content of 3%, is filledinto the melting furnace 9. The amount of material 10 must be adequateto fill the casting mould 7 adequately in liquid form to allow thetubular portion 29 to be completely filled. The melting furnace 9 isthen heated to a temperature above the melting point of the material 10,for example to 715° C. At the same time, the casting mould 7 ispreheated to a temperature of, for example, 350° C., in order to be ableto control the later solidification behaviour of the melt 10 in thecasting mould 7.

As soon as the temperature measuring elements 21, 39, 43, 45, 47indicate the suitable temperature, the initial casting can commence. Bymeans of the rod 19, the plug 17 closing the outlet opening 13 on theunderside of the smelting furnace 9 is raised, so that the metallic melt10 can flow through the outlet opening 13 into the first subvolume 27 ofthe casting mould 7 located under it. The melt 10 is thereby alsodistributed into the tubular portion 29, which is connected with itsfirst end 31 to the first subvolume 27 of the casting mould 7. Since thetemperature of the casting mould 7 lies below the melting point, themelt begins to solidify in the casting mould 7. This takes place atfirst at the wall of the casting mould 7, which is colder in relation tothe melt, and after that proceeds inwards. As a result of the smalldiameter at the second end 33 of the tubular portion 29, the furthestdistance from the first subvolume 27 and/or suitable temperature controlby the heating or cooling system 37, the melt 10 solidifies first at thesecond end 33 of the tubular portion 29, into which the measuringelement 35 extends. The solidification has the effect that anon-positive, and consequently tension-resistant, connection formsbetween the solidified melt 10 and the measuring element 35. During thesolidifying, the metallic material 10 contracts. This manifests itselfin particular in the direction of extent of the tubular portion 29. Thecasting mould 7 itself likewise contracts as it cools down, but manytimes less than the material 10, which passes through a phase transitionfrom liquid to solid. Therefore, the measuring element 35 is drawn intothe tubular portion 29 by means of the tension-resistant connectionbetween the solidified melt 10 and the measuring element 35.

In the radial direction, the shrinkage of the solidifying material inthe tubular portion 29 is scarcely noticeable. The tapering of thetubular portion 29 then prevents frictional effects between the wall ofthe casting mould 7 and the solidified material 10. This is so becausethe taper angle causes the material immediately to become detached fromthe wall, and not to pull itself along the wall, as a result of thenotable shrinkage in the axial direction. As a result, the measurementof the tensile force on the measuring element 35 becomes many times moreaccurate than when conventional devices are used. It is then possible touse the measuring element 35 to measure the tensile force that theshrinkage of the material 10 brings about, or the change in length ofthe material 10.

During the solidification, the temperature at the hotspot, i.e. theconnecting region between the first subvolume 27 and the tubular portion29, is also recorded. In this region, the melt 10 remains liquid for thelongest time, and the probability of the occurrence of a hot crack isgreatest here. For the temperature measurement, a temperature measuringelement 41 is telescopically or endoscopically led through the firstsubvolume 27 into the connecting region between the first subvolume 27and the tubular portion 29 through a bore in the casting mould 27. Thetemperature measuring element 41 is heat-resistant and is provided withcorresponding material, such as ceramic.

During the solidification, the readout system 25 controlled by thecomputer 23 reads both the temperatures measured with the temperaturemeasuring elements 39, 41, 43, 45, 47 as a function of time and thetensile force on the measuring element 35, or the change in position ofthe latter, measured with the force or position measuring instrument 57.

FIG. 4 shows the results of two tests, which were carried out in eachcase with a magnesium melt with an aluminium content of 3%, a meltingtemperature of 750° C. and a casting mould temperature of 350° C. Thetensile force and the hotspot temperature are plotted against time. Thesolid curves relate to the first test and the broken curves relate tothe second test. The arrows respectively show the axes applicable to thecurves. After a relatively steep rise at the beginning of thesolidification phase, the force increases approximately constantly, thetemperature behaving in the correspondingly opposite sense. After aninitial rise in temperature at the beginning to over 600° C. and a steepfall at the beginning of the solidification phase to about 500° C., thetemperature decreases relatively constantly. It is found that theapparatus according to the invention allows for the first time areproducible quantitative determination of hot tearing susceptibility,since the measurement results of the two tests coincide within thelimits of measurement error.

The occurrence of a hot crack would show itself in the force curve as astep or a short fall. Consequently, the maximum tensile force that ismeasured in a test is dependent on whether one or more hot cracks haveoccurred and the form and extent they have. Consequently, the maximumforce that is measured after a defined solidification interval is aquantitative measure of the size and/or number of hot cracks. Forexample, it has been found that, in the case of a magnesium melt with analuminium content of 1% and a hotspot temperature of 300° C., a tensileforce of less than 900 N indicates a large existing hot crack. Visualobservations have confirmed this. A crack of just a moderate size hereallows a tensile force of 900 N to 1100 N to be measured and the absenceof a hot crack or the presence of only very small hot cracks allowstensile forces of more than 1100 N to be measured.

The preferred forms of the invention described above are to be used asillustration only, and should not be utilized in a limiting sense ininterpreting the scope of the present invention. Obvious modificationsto the exemplary embodiments, as hereinabove set forth, could be readilymade by those skilled in the art without departing from the spirit ofthe present invention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and access the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention set forth in thefollowing claims.

1. Apparatus for determining the hot tearing susceptibility of metallicmelts, said apparatus comprising: a casting mould with a first subvolumeand a second subvolume, the second subvolume being formed as a tubularportion with a first end and a second end, the first end being connectedto the first subvolume, a measuring element that extends into the secondend of the tubular portion, and a measuring device for recording a forceon the measuring element and/or a change in position of the measuringelement in the direction of extent of the tubular portion, the measuringdevice being coupled with the measuring element, the tubular portionpresenting a cross-sectional area that is reduced in the direction ofthe second end for each and every subportion of the tubular portion thatmay be selected substantially over the entire length of the tubularportion.
 2. Apparatus according to claim 1, the tubular portionextending substantially in a horizontal direction.
 3. Apparatusaccording to claim 1, and a plurality of temperature measuring elementsassociated with the casting mould and arranged along the direction ofextent of the tubular portion.
 4. Apparatus according to claim 3, atleast one of the plurality of temperature measuring elements beingarranged in the first subvolume.
 5. Apparatus according to claim 4, thefirst subvolume including a heating device.
 6. Apparatus according toclaim 4, the first subvolume including a cooling device.
 7. Apparatusaccording to claim 4, and a heating or cooling system associated withthe casting mould so that the temperature of the casting mould can becontrolled.
 8. Apparatus according to claim 7, the heating or coolingsystem being associated with substantially the entire outer surface areaof the casting mould so that the temperature of the casting mould can besuitably controlled both in the first subvolume and in the tubularportion.
 9. Apparatus according to claim 3, the tubular portionincluding a heating device.
 10. Apparatus according to claim 3, thetubular portion including a cooling device.
 11. Apparatus according toclaim 1, and at least one temperature measuring element associated withthe casting mold.
 12. Apparatus according to claim 11, the at least onetemperature measuring element being arranged in the first subvolume. 13.Apparatus according to claim 1, the first subvolume including a heatingdevice.
 14. Apparatus according to claim 1, the first subvolumeincluding a cooling device.
 15. Apparatus according to claim 1, thetubular portion including a heating device.
 16. Apparatus according toclaim 1, the tubular portion including a cooling device.
 17. Apparatusaccording to claim 1, and a heating or cooling system associated withthe casting mould so that the temperature of the casting mould can becontrolled.
 18. Apparatus according to claim 17, the heating or coolingsystem being associated with substantially the entire outer surface areaof the casting mould so that the temperature of the casting mould can besuitably controlled both in the first subvolume and in the tubularportion.
 19. Apparatus according to claim 1, and a venting openingprovided at the second end of the tubular portion.